In this passage Joseph Smith made several stylistic changes in his editing for the 1837 edition. First, he changed the verb phrase from the active to the passive, which then required him to delete the reflexive direct object himself. He also replaced the perfect auxiliary hath with the modal verb shall, probably under the influence of the shall in the following clause (“then shall the fullness of the gospel of the Messiah come unto the Gentiles”).
All three of these changes are stylistic rather than grammatical. Elsewhere the text still maintains the kinds of expressions that Joseph Smith edited here in 1 Nephi 15:13. Note, in particular, that everywhere else the text says that the Savior will “manifest himself” (23 times), never that the Savior will “be manifested”. Although no other passage refers to his manifestation “in body”, six do refer to him as manifesting himself “in the flesh”:
There are three passages where the phraseology includes the verb make. One of these is in the passive; the two others are in the active and use the reflexive direct object himself:
Thus Joseph Smith’s editing in 1 Nephi 15:13 created a unique reading. He could have used the expression “to make manifest” in his editing of this passage (namely, in the passive: “the Messiah shall be made manifest in body”), which would have been more consistent since “to make manifest” is used in the text. Nonetheless, such editing would have still been exceptional since the text always uses the active form with the reflexive direct object when referring to Christ’s physical appearances.
Similarly, there is no need for the change from the perfect hath to the modal verb shall. The use of the present perfect in clauses referring to the future are found elsewhere, including the following nearby examples:
Summary: Restore the original phraseology in 1 Nephi 15:13 (“after that the Messiah hath manifested himself in body unto the children of men”); the verb manifest is always used in the active voice when referring to Christ’s physical appearances; elsewhere the text sometimes uses the present perfect in an after-clause to describe a future event.